Chorionic Villus Sampling (CVS)

Test Overview

Chorionic villus sampling (CVS) is a test done during early pregnancy that can find certain problems with your baby (fetus). It is generally done when either you or the father has a disease that runs in the family (genetic disorder). It may also be done when you are over age 35—being over 35 increases your chance of having a baby with a chromosome defect.

Chorionic villi are tiny finger-shaped growths found in the placenta. The genetic material in chorionic villus cells is the same as that in the baby's cells. During CVS, a sample of the chorionic villus cells is taken for biopsy. The chorionic villus cells are checked for problems. The procedure is generally done late in the first trimester, most often between the 10th and 12th weeks.

The chorionic villus sample can be collected by putting a thin flexible tube (catheter) through the vagina and cervix into the placenta. The sample can also be collected through a long, thin needle put through the belly into the placenta. Ultrasound is used to guide the catheter or needle into the correct spot for collecting the sample.

If you have a family history of certain diseases, CVS can be used to find genetic disorders, such as Tay-Sachs disease or hemophilia. It can also find chromosomal birth defects, such as Down syndrome. CVS cannot find neural tube defects, and it cannot be used to see if the baby's lungs are mature.

Chorionic villus sampling can be done earlier in pregnancy (at 10 to 12 weeks) than amniocentesis (usually done at 15 to 20 weeks). This allows you to know the health of your baby and make an earlier decision whether to continue or end the pregnancy. Results of CVS can be available sooner than amniocentesis results.

You or the baby's father has a family history of a genetic disorder or birth defect.

Screening tests suggest that your chance of having a baby with a genetic disorder or birth defect is higher than average.

How To Prepare

You may be asked to drink a glass of fluid about an hour before the test so that your bladder is full. A full bladder makes it easier to do the test.

You will be asked to sign a consent form that says you understand the risks of the test and agree to have it done.

Talk to your doctor about any concerns you have regarding the need for the test, its risks, how it will be done, or what the results will mean. To help you understand the importance of this test, fill out the medical test information form(What is a PDF document?).

Be sure to tell your doctor if you are allergic to any medicines, such as numbing medicines (local anesthetics), before the procedure.

How It Is Done

Chorionic villus sampling is most commonly done by a perinatologist in the doctor's office or the hospital. An overnight stay in the hospital usually is not needed unless problems occur during the procedure.

Transabdominal (through the belly) chorionic villus sampling or transcervical (through the cervix) chorionic villus sampling can be done. The choice may depend on where the fetus and placenta are in the uterus.

Through the belly (transabdominal)

You will lie on your back on an examination table with your belly bare.

Gel will be rubbed on your belly to use with the ultrasound unit. An ultrasound device (transducer) that gives off and picks up sound waves will be passed over your belly. The reflected sound waves are sent to a computer to make a picture of the uterus, your baby, and the placenta on a screen. Your doctor or an ultrasound technician will look at the picture on the screen to help guide the needle used to collect a sample of the chorionic villus. Your baby's heart rate can also be checked during the procedure using ultrasound. For more information, see the topic Fetal Ultrasound.

Your skin where the needle will be put in is cleaned with alcohol and numbed with a medicine. Your doctor then puts a long thin needle through your belly and uterus to the placenta and collects a sample of the chorionic villus cells.

After the sample is collected, your doctor may listen to your baby's heart rate and check your blood pressure, pulse, and breathing.

Through the cervix (transcervical)

You will be asked to take off your clothes below the waist and drape a covering around your waist. You will then lie on your back on an examination table with your feet raised and supported by stirrups. This allows your doctor to look at your genital area.

Your doctor will put an instrument with curved sides (speculum) into your vagina. The speculum gently spreads apart the vaginal walls, allowing the inside of the vagina and the cervix to be seen. The cervix will be cleaned with a special soap.

An ultrasound will be used to help your doctor guide the catheter through your cervix to the placenta. An ultrasound device (transducer) that gives off and picks up sound waves will be passed over your belly. The reflected sound waves are sent to a computer to make a picture of the uterus, your baby, and the placenta on a screen. Your baby's heart rate can also be checked during the procedure using ultrasound. For more information, see the topic Fetal Ultrasound.

When the catheter is correctly placed, a sample of chorionic villus cells will be collected.

After the sample is collected, your doctor may listen to your baby's heart rate and check your blood pressure, pulse, and breathing.

How It Feels

If you have the procedure through the belly, you will feel a short, sharp sting from the needle used to give the numbing medicine. There is usually no pain when the collecting needle is put in the belly. You may feel some cramping when the needle is inside your uterus.

Most women do not find the transcervical procedure painful. You will probably find that this test feels similar to having a Pap test or pelvic examination. You may feel some cramping when the catheter is guided through your cervix.

Risks

Chorionic villus sampling (CVS) can cause cramping, leakage of amniotic fluid, and vaginal spotting, which goes away in 1 to 2 days. You may feel some soreness where the needle was put in if you had the belly procedure done.

CVS also increases the chance of:

Developing a uterine infection.

Having a miscarriage. Overall, one study showed the risk of miscarriage from CVS is about 1 in 400 when done by a highly trained provider.1

Having a baby with arm or leg abnormalities though the chance of this happening is very low, especially when the test is done after 10 weeks.

Chorionic villus sampling has a very small chance of causing bleeding that could result in mixing your blood and your baby's. If you have Rh-negative blood, you will be given the Rh immunoglobulin vaccine (such as RhoGAM) to prevent Rh sensitization which could harm your baby if he or she has Rh-positive blood.

After the procedure

It is normal to have mild cramping, leakage of a small amount amniotic fluid, and vaginal spotting for the first day or two after the procedure. Call your doctor immediately if you have:

Results

Cells from your baby are looked at carefully for the proper number and arrangement of the genetic material (chromosomes) that show genetic diseases. Normally there are 46 chromosomes in each cell, arranged in 23 pairs. Chromosomes also tell the sex of your baby. It may take 1 to 2 weeks to get CVS results.

Chorionic villus sampling (CVS)

Normal:

No abnormalities are found in the genetic material of the chorionic villus cells.

Abnormal:

Abnormalities are found in the genetic material of the chorionic villus cells.

What Affects the Test

In rare cases, the chorionic villus cells may have abnormal genetic material even though the baby's cells are normal. This is called a false-positive result. An abnormal test result may need to be confirmed by amniocentesis.

What To Think About

Amniocentesis (which is usually done later in the pregnancy than CVS) can also be used to find other diseases of the fetus, such as neural tube defects. If CVS does not show clear results, amniocentesis may need to be done.

CVS is done if you are at high risk for having a baby with a chromosomal birth defect (such as Down syndrome) or a family genetic disease (such as Tay-Sachs disease or hemophilia). The benefits of this test often outweigh the risks. Genetic diseases and birth defects can be found earlier in pregnancy by CVS than by amniocentesis. This allows you to make an earlier decision whether to continue or end the pregnancy.

The results of CVS may vary depending on how the sample was taken.

If you have a vaginal infection (such as a vaginal yeast infection or genital herpes), a belly procedure will be used instead of a vaginal procedure.

CVS causes bleeding that could lead to mixing of your blood and your baby's about half of the time. If you have Rh-negative blood, you will be given the Rh immunoglobulin vaccine (such as RhoGAM) to prevent Rh sensitization which could harm your baby if he or she has Rh-positive blood.

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